Mental and matter exist, but do not interact

In order to avoid the interaction problem, some philosophers took the position that both, immaterial (mental) and material (brain) substance exist independently, but they do not interact. This view is called parallelism and was first formulated by a follower of Descartes, Geulinx, but is more often associated with the philosopher Leibniz. The obvious problem here is that it certainly appears that there is a causal relation between body and mind (it is normally assumed that an injury is the cause of the subsequent pain, and that feeling pain makes one scream). To explain this, Leibniz proposed that God arranged this in advance, so that the mind and body act synchronously (the so-called doctrine of pre-established harmony). Thus, the experience of pain is not caused by the injury, it is prearranged that one event parallels the other. Such a ‘deus ex machina' explanation seems highly implausible. One would expect that a being capable of instituting ‘pre-established harmony' would also be able to find a way to allow the interaction between mind and body - surely a more elegant solution. A similar (but perhaps even more bizarre) view is known as occasionalism, proposed by Malebranche. He suggested that whenever he wanted to move his arm, for example, it was actually moved by God rather than his volition. This would make God very busy indeed.

The virtue of dualism is that it is less reductive than materialism and corresponds better to common sense. It can account for the qualitative difference between mental processes and brain processes as commonly experienced. Yet, dualism also seems to be a dead-end in many respects.